The present invention relates to a demineralization apparatus and a cloth for packing a diluting chamber of the demineralization apparatus. Particularly, it relates to an improvement in a demineralization apparatus utilizing electrodialysis action.
As a method of producing demineralized water, an ion exchange resin method which comprises passing water to be treated through an ion exchange resin-packed bed, regenerating a deteriorated ion exchange resin with an acid or alkali regenerant and then using the regenerated resin repeatingly has been used generally. However, the method has a drawback in that a regeneration process for the ion exchange resin by using regenerant like hydrochloric acid or caustic soda is troublesome and, in addition, a great amount of alkaline and acidic waste water is discharged. Accordingly, a process for producing demineralized water without using the regenerant has been demanded.
For such a demand, a demineralization method comprising an ion exchange resin and an ion exchange membrane in combination has been proposed in recent years. Based on the fact that water-containing ion exchange resins are good electric conductors, an electrodialysis action using anion and cation exchange membranes as diaphragms is utilized in this method. In this method, ion exchange resins as a filler are filled or packed in a diluting chamber of an electrodialysis unit defined with an anion exchange membrane and a cation exchange membrane, and water to be treated flows through the diluting chamber under application of a voltage, and the treated water is obtained as demineralized water.
During processing of this method, impurity ions in water to be treated is subjected to ion exchange by the ion exchange resin, impurity ions captured by the ion exchange resin are eluted by supply of electric current, the eluted impurity ions are separated by the ion exchange membranes. Demineralized water is produced while conducting ion exchange by the ion exchange resin and regeneration thereof simultaneously.
In this way, according to a so-called electrodemineralization method of producing demineralized water by using the ion exchange membrane and the granular ion exchange resin as the filler, it requires neither the regeneration operation for the granular ion exchange resin nor use of regenerant of acid or alkali for regeneration. Therefore, it can be considered as an advantageous method.
However, the apparatus used for the known electrodemineralization method described above has a drawback that there is a risk that the granular anion ion exchange resin and the granular cation ion exchange resin in a mixed state would separate (granular anion and cation exchange resins homogeneously dispersed and mixed are made into an inhomogeneous dispersed state due to the difference in the specific gravity between both of the resins), upon change of flow rate of water to be treated, or upon operation of discharging suspended materials accumulated in the diluting chamber out of the system. If the separation of the mixed granular ion exchange resins occurs, demineralized water of stable quality can no more be obtained.
In view of the above, there is proposed in Japanese Patent Publication (KOKOKU) No. 4-72567 (1992), a means for finely dividing a diluting chamber (deionization chamber) into a specific size to prevent the separation of the mixed granular ion exchange resins caused by fluidization of the mixed granular ion exchange resins, so that there is a disadvantage of complicating the apparatus and making the maintenance and administration troublesome.
As a result of studies made by the present inventors, it has been found that troublesome maintenance operation can be made unnecessary and demineralized water having excellent quality can be obtained stably, by using as ion exchangers in the dilution chamber, a mixture of strongly acidic cation exchange fibers, strongly basic anion exchange fibers and ionically inactive synthetic fibers in the form of cloth. This present invention has been accomplished based on the finding.